1. Field of the Invention
The present invention relates to a micromirror device, and more particularly, to a micromirror device made in a simple structure using interdigitated cantilevers and having bistable rotational states, and applications thereof.
2. Background of the Invention
Typical micromirror devices for image display are two-dimensionally arranged on a substrate on which an addressing circuit is fabricated, and are driven by electrostatic force to reflect incident light at a predetermined angle. These micromirror devices can be utilized in optical information processing, image display devices, such as projection displays, video and graphics monitors, television, or optical scanning devices such as copiers.
One example of conventional micromirror devices is disclosed in U.S. Pat. No. 5,535,047 which was issued to Larry J. Hornbeck on 9 Jul. 1996. FIG. 1 is an exploded perspective view of a conventional micromirror device for image display. Referring to FIG. 1, on an addressing circuitry is disposed a first layer including a yoke address electrode 10 and a landing site 11. On the first layer is disposed a second layer supported by an address support post 12 and including a mirror address electrode 13, a torsion hinge 14, and a yoke 15 directly contacted with a mirror 17. The mirror 17 is disposed on the second layer and is coupled with the yoke 15 through a mirror support post 16. Thus, the micromirror device is comprised of four layers including the addressing circuitry, and includes the support post for supporting the mirror address electrode layer, the support post for supporting the mirror, the yoke connected to the mirror, the torsion hinge, one yoke address electrode for applying a voltage between the yoke address electrode and the mirror, and two address electrodes for driving the mirror.
FIG. 2 is a cross sectional view of the micromirror device of FIG. 1 taken along a center line of the length direction of the hinge, and shows a connection state of the mirror 17, the yoke 15, the hinge 14 and the respective layers. Referring to FIG. 2, the mirror 17 is connected to the yoke 15 through the mirror support post 16. The hinge 14 is disposed beneath the yoke 15 and serves as a rotational shaft. The address electrode 10 is connected with the support post 12, and after it is processed to form an addressing circuitry, it is also connected to a substrate 6 partially coated with a passivation oxide film 8.
FIGS. 3A and 3B are cross sectional views of rotating appearances of the mirror taken along a line normal to the center line of the length direction of the hinge. In FIGS. 3A and 3B, reference numerals of elements that are not related with description of the art are intentionally omitted. When a potential difference is applied between the mirror 17 and the one electrode 10, the mirror 17 is rotated in one direction by the electrostatic force as shown in FIG. 3A, and after it is rotated by a predetermined angle, it is collided with the landing site 11 and is then stopped. On the other hand, when a voltage is applied between the mirror 17 and the other electrode 10, the mirror 17 is rotated in an opposite direction as shown in FIG. 3B. Thus, the mirror 17 has bistable condition, and a reflecting angle of the light becomes different depending on the two rotational states of the mirror. Accordingly, by changing a traveling path of the light that is incident from a constant direction with the micromirror, it is possible to allow the light to be incident into a lens (not shown) and a screen (not shown) or to be deviated from the screen.
As described above, since the conventional micromirror device is comprised of the mirror, the yoke, the hinge, and the respective support posts, and thus has a complicated structure, there is a disadvantage in that too many processes are requested in order to fabricate the micromirror device. Hence, there are difficulties in driving the mirror at a constant power, and fabricating the mirror, so that fabrication cost becomes high.
Further, in the conventional micromirror device, since the mirror is always rotated in two directions of the left direction and the right direction by suitable voltages applied to the mirror address electrode, the hinge is always in a distorted state. Since such an operation is carried out by a pair of thin hinges, rigidity of the hinges acts as a main factor determining a characteristic of the mirror.